Karen Francis, a key architect of General Motors Corp.’s campaign to reinvigorate its vehicle brands, is leaving the automaker for an Internet marketing post.

Francis, 38, is stepping down as marketing general manager of Oldsmobile to become chief marketing officer and managing director of Internet Capital Group, an electronic business-to-business company based in Pennsylvania.

She will be based in San Francisco. With close ties to outgoing GM director John Smale and North American chief Ronald Zarrella, her departure is a setback for GM’s ongoing efforts to reposition its brands and rebuild its slumping U.S. market share.

“It’s a disappointment. Karen carries a high amount of credibility with senior GM management,” said David Fischer, a GM dealer in Troy. “She navigated the GM fortress quickly and brought a positive new light to a changing brand.”

Francis, one of three females heading GM car divisions, joined GM in 1996 as part of a high-profile class of outsiders hired to revitalize its car and truck lineup.

After launching the new Chevrolet Venture minivan in 1996 with the motto “Let’s go!,” Francis moved on to run Chevrolet’s 11-state Rocky Mountain sales region.

In January 1996, she became marketing general manager of Oldsmobile, GM’s oldest division. Seeking younger buyers, the division shed its venerable lineup of boxy family sedans and wagons in favor of slicker sedans and coupes. The average age of a new Oldsmobile buyer has dropped from 62 to 49.